Peripheral sensors for occupant protection systems mostly use current interfaces (for example, PAS4, PSI5) for transmitting sensor data to a central control unit (ECU) in a vehicle. The latest generation of current interfaces (PSI5) uses synchronization to allow bus operation with multiple sensors at a receiver. For the function of the synchronization, the central control unit (ECU) generates an operating cycle in the form of a voltage pulse which is detected by the sensors on the bus and indicates the start of a new data transmission cycle. This voltage pulse is referred to as a synchronization pulse and is generated with the aid of current sources and current sinks which charge and discharge the bus load. This voltage pulse is typically repeated every 500 μs.
In order for a synchronous bus system having one sensor or multiple sensors to function, it is important for the synchronization pulse to have a certain shape and a certain time behavior for all possible bus configurations and under all possible operating conditions. Therefore, known synchronous bus systems generally use a trapezoidal synchronization pulse PT having a predefined edge steepness, as shown in FIG. 3. The edge steepness lies between an edge steepness of a first characteristic curve, which represents a lower limit Vu, and an edge steepness of a second characteristic curve, which represents an upper limit Vo. During synchronous bus operation, the trapezoidal shape of synchronization pulse PT results in increased electromagnetic radiation (EMC) in the frequency spectrum of the signal transmission, due to the high harmonic content. This may be counteracted to a certain extent, for example, by a synchronization pulse PTr shown in FIG. 4, which has a trapezoidal shape having four rounded vertices.
German Patent Application No. DE 10 2009 001 370 A1 describes a reception device for receiving current signals, a circuit system having such a reception device, and a method for transmitting current signals via a bus system. The described reception device includes at least two bus connecting devices for receiving current signals of multiple transmitters, each bus connecting device being designed for connecting to at least one bus connection, and a control device for outputting synchronization pulses to the bus connecting devices for synchronizing the transmitters. The bus connecting devices output the synchronization pulses with at least one time offset with respect to each other to the multiple transmitters, each of the synchronization pulses having a trapezoidal shape having rounded vertices.